Numerous molded articles and films are manufactured from one or more of a variety of polymeric resins. Typically, these resins must be blended with other, “additive” components to enable the production of an end-use material having specified physical, chemical, and/or mechanical characteristics. Thus, for example, it is well-known that the impact properties of resins such as poly(vinyl chloride) (“PVC”) can be markedly improved through the addition of compounds such as core-shell polymers : These include acrylic impact modifiers (“AIMs”) as well as methyl methacrylate-butadiene-styrene (“MBS”) modifiers. AIMs have cores based on alkyl acrylates, while MBS modifiers have cores consisting largely of butadiene-styrene copolymers or butadiene homopolymers. Shells for both types of modifiers usually consist of polymethyl methacrylate homopolymers or methyl methacrylate-styrene copolymers. Similarly, it is known that the ability to process resins such as PVC to form films or end-use molded articles can be enhanced or enabled through the addition of compounds such as polymeric (typically methyl methacrylate-based) processing aids (“PAs”).
Such additives are typically made by emulsion polymerization and then dried to a powder form before being blended with the polymeric resin substrate/matrix. Thus, the ability to isolate a composition has been an accepted limitation upon the selection of new additive compositions. Typically, this limitation is addressed through the use of multistaged polymer compositions, where the outer-stage shells have a relatively high Tg (sometimes referred to as being “hard”) to provide isolation capabilities, while the inner stages (e.g. the “rubbery” cores) provide much of the functionality. Alternatives to the traditional powder-form additive systems have been proposed—but none have proven particularly viable, and many relate to additives other than AIM, MBS or PA type additives.
U.S. Pat. No. 3,864,432 describes the combination of ethylene/vinyl acetate copolymer latexes with polymeric resins such as PVC, PVC/vinyl acetate, and polyethylene to achieve pourable powders of elastomer-treated thermoplastics. The only “additive” systems exemplified by this patent relate to ethylene/vinyl acetate elastomers. While this patent teaches that PVC mixed with the ethylene/vinyl acetate latexes results in a pourable powder (the object of the invention), the patent fails to describe any impact performance (if any) resulting from the use of the latexes.
U.S. Pat. No. 3,067,162 teaches the combination of dilute aqueous dispersions of resin matrix with aqueous dispersions of plasticizers, such as diethylhexylphthalate. The plasticizer is then slowly absorbed by the resin particles. The resin/plasticizer granules are then separated from the aqueous phase by filtration, and dried by conventional methods. The process taught in this patent is slow and requires a number of additional steps beyond mixing the components as originally made or available: (1) aqueous dispersions of the components (both resin and plasticizer) must be prepared; (2) the removal of substantial amounts of water is required; and (3) after the water is removed the product must be separately dried. Furthermore, this patent does not teach the use of aqueous-form AIM, MBS or PA additives.
U.S. Pat. No. 3,813,259 discloses a process to achieve resin-coated elastomer particles where a dilute resin latex is slowly coagulated onto an elastomeric slurry, within very specific temperature ranges—allowing the resin to fuse both to itself and to the elastomer, without actually melting. This process is time consuming, and requires the use very dilute latexes of the resin (i.e. 0.1 to 8% solids), thus involving the eventual removal of substantial amounts of water. Furthermore, the coagulation process must be carefully monitored to prevent the latex from coagulating as a separate phase rather than as a coating on the elastomeric particles.
In-situ polymerization of matrix resin monomer in presence of a modifier latex is taught in U.S. Pat. No. 4,272,424. Such methods suffer a number of drawbacks. The presence of the modifier latex can adversely affect the polymerization of the matrix monomer, leading to coarse particles and the deposition of polymer scale on the walls of the polymerization reactor. Furthermore, the water that is eventually removed from the reaction mixture can contain varying amounts of un-incorporated modifier latex—causing potential environmental problems. Furthermore, such methods do not provide a sufficient degree of flexibility to the matrix resin compounder, who blends the matrix resin in various formulations (depending on the end-use) with various levels of additives.
The “artificial” emulsification of various processing lubricants, stabilizers and fillers, for use in subsequent blending with matrix resins, is taught in references such as U.S. Pat. No. 4,040,997 and U.S. Pat. No. 5,334,644. The additives at issue in these references are not generally made from emulsion techniques, and thus must be obtained in commercially available form (typically solid) and subjected to specific conditions where they are emulsified. These references do not address the use of AIM, MBS or PA compositions, which are ordinarily made in emulsion form and thus require no additional process steps for use in emulsion-form.
U.S. Pat. No. 4,880,877 discloses an elaborate process whereby a latex of a graft rubber polymer can be blended with a thermoplastic resin. The process is elaborate and requires the graft rubber polymer be mixed with an organic solvent; followed by the removal of the aqueous phase from the mixture; followed by the addition of the matrix resin to the organic phase of the mixture; followed by the removal of the organic solvent (and any residual water); followed by still further processing. The disclosed process is cumbersome and involves the use of organic solvents, which can present environmental, health and safety hazards.
EP 735,078 A1 describes a method of producing impact-modified thermoplastics by introducing an emulsion of an elastomeric polymer with a thermoplastic resin in a screw machine. However, rather than combine emulsion-form elastomeric polymers directly with the matrix resin, EP 735,078 teaches that the elastomer emulsion must first be subjected to an elaborate mechanical dewatering process before it can be combined with the matrix resin. Thus, by the time the elastomer emulsion is actually combined with the matrix resin, it has been freed of most of its water and basically exists in a powder form.
Accordingly, an object of the present invention is to provide for the convenient use of aqueous-form AIM, MBS and PA additives. A further object of the present invention is to provide for new additive compositions that would not otherwise be available in powder-form. A further object of the present invention is to provide matrix-resin compounders with a great deal of flexibility in their formulation of end-use blends. A still further object of the present invention is to provide for the reduced cost in the production of AIM, MBS, and PA compositions, and reduced cost in the formulation of matrix resins with additives.